1. Field of the Invention
The present invention relates to flexible printed circuit boards having conductor paths on both sides of each insulating sheet and having at least one through-contact, whereby the through-contact is produced by a metal coating about the hole.
2. The Prior Art
Where printed circuit boards carry conductor paths on both sides thereof, through-contacts whereby conductors on opposite sides of the insulating layer are electrically contaced are generally produced by drilling through the board and the conductors and metallizing the walls of the hole via vapor deposition. Producing such contact through a wet chemical or vapor deposition process is wasteful of material and costly. It is also a disadvantage that the entire board is coated and reinforced, reducing the flexibility of the circuit board.
Another form of through-contact has been effected by forming a hole by radial cuts having three or four segments, with the tongues being pushed through to the opposite side of the board. Terminal pins may be inserted through the holes, whereafter solder is flowed into the hole. Where terminal pins are not used, the tongues are laid over onto the undersurface of the board before soldering. Hole-punching dies having the necessary cutters are expensive to produce, and the solder flow between the segmented tongues is restricted. Cracks formed in the tongues during deformation often impede the flow of solder, reducing the mechanical and electrical reliability of the through-contact.